commander: forgot to close fd

src/modules/commander/commander.cpp

@@ -2762,6 +2762,7 @@ int commander_thread_main(int argc, char *argv[])
 	px4_close(diff_pres_sub);
 	px4_close(param_changed_sub);
 	px4_close(battery_sub);
+	px4_close(land_detector_sub);
 
 	thread_running = false;